An optical element has conventionally been known which has a separation layer for circular light polarization comprising a cholesteric liquid crystal layer showing such circular dichroism that natural light is separated thereby into reflected light comprising circularly polarized light and transmitted light, and in which the circularly polarized light is converted to linearly polarized light with a quarter-wavelength plate. This element has an advantage that since the light emitted by a light source can be supplied as linearly polarized light to a polarizing plate, the absorption loss in the polarizing plate can be reduced to thereby improve the brightness of a liquid crystal display.
However, such conventional optical elements have a problem that the display appears to be colored when viewed from slant directions. It has been proposed to mitigate this problem concerning viewing angle by disposing a quarter-wavelength plate on the longer-helical-pitch side of a cholesteric liquid crystal layer having Grandjean orientation (see PCT Publication WO97/19385). However, this technique is unsuitable for practical use because the improvement in viewing angle characteristics is insufficient for application to liquid crystal displays and the like. Specifically, when the thus-improved liquid crystal display or the like is viewed while gradually shifting the viewing angle linearly, for example, from the front to a slant direction, it appears to undergo a considerable color change or to change its color from blue to an utterly different color of red.